U.S. patent number 4,492,949 [Application Number 06/476,685] was granted by the patent office on 1985-01-08 for tactile sensors for robotic gripper and the like.
This patent grant is currently assigned to Barry Wright Corporation. Invention is credited to Peter N. Cholakis, Robert R. Peterson, Dale W. Schubert.
United States Patent |
4,492,949 |
Peterson , et al. |
January 8, 1985 |
Tactile sensors for robotic gripper and the like
Abstract
A tactile sensor for sensing an object in contact therewith. In
its preferred form, the sensor comprises a plurality of layers
disposed in a sandwich arrangement. A top layer is comprised of a
flexible, electrically-insulating material and a plurality of
parallel flexible conductive rods. A bottom layer is comprised of
an electrically-insulating material and a plurality of parallel
conductive rods that extend at right angles to the conductive rods
of the top layer, thus forming a sensory array comprising a
plurality of superimposed intersection points arranged in a grid
pattern. An intermediate layer is comprised of a resilient,
electrically-insulating material in which is disposed a plurality
of parallel conductive posts that extend perpendicular to the plane
of the three layers. These posts are comprised of a resilient
conducting material. Each conductive post is disposed at one of the
sensor's aforementioned intersection points so as to electrically
couple one of the conductive rods of the top layer to one of the
conductive rods of the bottom layer. The conductive rods are formed
with a selected cross-section, in order that changes in the amount
of pressure exerted on the sensor will produce corresponding
logarithmic exchanges in the contact surface area, and hence
electrical contact resistance, established between the conductive
rods and those conductive posts disposed beneath the points of
pressure.
Inventors: |
Peterson; Robert R. (Hudson,
MA), Schubert; Dale W. (Sudbury, MA), Cholakis; Peter
N. (Hopkinton, MA) |
Assignee: |
Barry Wright Corporation
(Newton Lower Falls, MA)
|
Family
ID: |
23892841 |
Appl.
No.: |
06/476,685 |
Filed: |
March 18, 1983 |
Current U.S.
Class: |
338/114; 338/99;
73/862.046 |
Current CPC
Class: |
B25J
13/084 (20130101); G01L 1/205 (20130101); G01L
5/228 (20130101); H01H 13/702 (20130101); H01H
13/785 (20130101); G01L 1/18 (20130101); H01H
2239/078 (20130101); H01H 13/703 (20130101); H01H
2201/032 (20130101); H01H 2203/002 (20130101); H01H
2203/008 (20130101); H01H 2205/006 (20130101); H01H
2207/01 (20130101); H01H 2209/002 (20130101); H01H
2209/032 (20130101); H01H 2209/056 (20130101); H01H
2209/074 (20130101); H01H 2211/032 (20130101); H01H
2227/03 (20130101); H01H 2231/04 (20130101) |
Current International
Class: |
B25J
13/08 (20060101); G01L 5/22 (20060101); G01L
1/18 (20060101); G01L 1/20 (20060101); H01H
13/702 (20060101); H01H 13/70 (20060101); H01C
010/10 () |
Field of
Search: |
;338/114,99,100,101
;73/172,432R ;324/65R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2115555 |
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Sep 1983 |
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GB |
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2115556 |
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Sep 1983 |
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GB |
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Primary Examiner: Envall, Jr.; Roy N.
Assistant Examiner: Sears; C. N.
Attorney, Agent or Firm: Gilbert; Milton E. Ross; Gary E.
Pandiscio; Nicholas A.
Claims
What we claim is:
1. A tactile sensor for sensing the pressure impressed by an object
in contact therewith, said sensor comprising a sandwich having:
(a) a top layer comprised of a first flexible,
electrically-insultating material and a plurality of first
flexible, electrically-conductive rods disposed in parallel grooves
in said first electrically-insulating material;
(b) a bottom layer secured to said top layer, said bottom layer
being comprised of a second electrically-insulating material and a
plurality of second electrically-conductive rods extending parallel
to one another, said bottom layer being disposed relative to said
top layer so that said first rods extend across and substantially
parallel to said second rods; and
(c) an intermediate layer engaged by said top and bottom layers,
said intermediate layer being comprised of a selected material that
is both resilient and electrically-insulating and a plurality of
mutually-spaced electrically-conductive posts disposed in and
extending transversely through said selected material so that the
opposite ends of said posts confront said top and bottom layers,
said electrically-conductive posts being made of a resilient
material and being disposed so that the axis of each post
intersects one each of said first and second rods, whereby a matrix
of electrically conducting paths is provided by said first and
second rods and said posts.
2. A tactile sensor according to claim 1 wherein said first and
second conductive rods have a cross-sectional profile conforming
substantially to the cross-sectional profile shown in FIG. 3.
3. A tactile sensor according to claim 2 wherein said second
conductive rods are formed of a flexible material.
4. A tactile sensor according to claim 1 wherein the said
conductive rods of at least one of said top and bottom layers are
made of a resilient material and have a hardness greater than the
hardness of said intermediate layer.
5. A tactile sensor according to claim 4 wherein said first and
second electrically-insulating materials and said selected
electrically-insulating material all comprise a polymer, and said
conductive posts are comprised of a polymer compounded with a
conducting material.
6. A tactile sensor according to claim 3 wherein said conductive
rods comprise an elastomer.
7. A tactile sensor according to claim 6 having 16 conductive rods
in said top layer and 16 conductive rods in said bottom layer.
8. A tactile sensor for sensing an object in contact therewith,
said sensor comprising:
(a) a top layer made of a first flexible, electrically-insulating
material and including a plurality of first conductive rods
extending parallel to one another in a first plane, said first
conductive rods being flexible along their length and having a
cross-sectional profile conforming substantially to the profile
illustrated in FIG. 3;
(b) a bottom layer made of a second electrically-insulating
material and including a plurality of second conductive rods
extending parallel to one another in a second plane extending
substantially parallel to said first plane, said second conductive
rods having a cross-sectional profile conforming substantially to
the profile shown in FIG. 3, said bottom layer also being disposed
relative to said top layer so that said second conductive rods
extend at an angle to said first conductive rods, thus forming a
sensory array comprising a plurality of superimposed intersection
points arranged in a grid pattern; and
(c) an intermediate layer extending in a third parallel plane and
disposed between and engaged by said first and second layers, said
intermediate layer being made of a resilient material which is
electrically-conductive.
9. A tactile sensor according to claim 8 wherein said first and
second conductive rods are formed of the same material.
10. A tactile sensor according to claim 9 wherein said first
conductive rods and said second conductive rods have a hardness
greater than the hardness of said intermediate layer.
11. A tactile sensor according to claim 10 wherein each of said
first and second layers of electrically insulating material
comprise a polymer, and said intermediate layer comprises a polymer
compounded with a conducting material.
12. A tactile sensor according to claim 11 having 16 conductive
rods in said top layer and 16 conductive rods in said bottom
layer.
13. A tactile sensor according to claim 1 wherein said first
electrically-insulating material has an outer edge which is sealed
to said second electrically-insulating material so as to form a
sealed environment for said intermediate layer.
14. A tactle sensor according to claim 1 whrein said first and
second rods, said first electrically-insulating material, said
selected material and said posts are all made of a resilient
material, and further wherein said first and second rods have a
compression stiffness greater than that of said selected material
and said posts.
15. A tactile asensor according to claim 14 wherein said second
electrically-insulating material is substantially rigid.
16. A tactile sensor according to claim 14 wherein said second
electrically-insulating material is resilient.
17. A tactile sensor according to claim 13 wherein at least one of
said top and bottom layers is arranged so that at least said first
rods or said second rods are disengaged from said posts when said
tactile sensor is not subjected to compression by the pressure of
an object in contact therwith, whereby no electrical signal can
pass from said first rods to said second rods via said posts until
a predetermined non-zero pressure is applied to said sensor by an
object in contact therewith.
18. A tactile sensor according to claim 17 wherein at least said
first rods each have a cross-sectional shape that varies with
increasing distance from said posts so that the contact areas
between said first rods and said posts will increase as said first
rods and said posts are pressed together.
19. A tactile sensor according to claim 1 wherein said first and
second electrically-conductive rods are always engaged with said
intermediate layer.
20. A tactile sensor according to claim 1 wherein said first and
second conductive rods each have a cross-sectional configuration
that conforms substantially to the cross-sectional configuration
illustrated in FIG. 3.
21. A tactile sensor according to claim 1 wherein said bottom layer
comprises a plurality of electrically-conductive busses, and each
of said second rods is engaged with one of said busses.
22. A tactile sensor according to claim 21 wherein said busses
extend parallel to and are aligned with said second rods.
23. A tactile sensor according to claim 22 wherein said second
electrically-insulating material is rigid.
24. A tactile sensor according to claim 23 wherein said busses are
bonded to said second electrically-insulating material.
25. A tactile sensor to claim 8 wherein said first and second rods
engage opposite sides of said intermediate layer and said first and
second layers are bonded to one another.
26. A tactile sensor according to claim 1 wherein the opposite ends
of each of said posts engage selected ones of said first and second
rods, and further wherein said opposite ends of said posts have
cross-sectional shapes that vary so that the contact areas between
the opposite ends of said posts and said first and second rods will
increase as said first and second layers are pressed against said
intermediate layer.
27. A tactile sensor according to claim 26 wherein the opposite
ends of said posts have a cross-sectional configuration conforming
substantially to the cross-sectional configuration illustrated in
FIG. 3 of the attached drawings.
28. A tactile sensor according to claim 1 wherein said first rods
extend beyond the outer edge of said intermediate layer and are
bent so as to lie against said bottom layer.
29. A tactile sensor for sensing the pressure impressed by an
object in contact therewith, said sensor comprising:
(a) a top layer comprised of a first flexible,
electrically-insulating material and a first plurality of flexible
electrically-conductive rods extending parallel to one another in
grooves in said first electrically-insulating material; and
(b) a bottom layer comprised of a second electrically-insulating
material and a second plurality of electrically-conducting rods
extending parallel to one another;
said bottom layer being disposed relative to said top layer so that
the rods of said first plurality of rods extend across and directly
engage the rods of said second plurality of rods, whereby a
plurality of electrically-conducting paths is provided by said
first and second pluralities of rods;
the said rods of at least one of said top and bottom layers (a)
each being elastomeric and (b) each having a cross-sectional shape
that varies with increasing distance from the other of said top and
bottom layers so that the contact areas between the rods of said
first and second pluralities of rods will increase non-linearly as
portions of said layers are deformed as a consequence of being
pressed against one another.
30. A tactile sensor according to claim 29 wherein all of said rods
and at least one of said first and second electrically-insulating
materials is elastomeric.
31. A tactile sensor according to claim 30 wherein said second
electrically-insulating material is rigid.
Description
FIELD OF THE INVENTION
This invention relates to industrial robots in general, and more
particularly to tactile sensors for use in such robots.
BACKGROUND OF THE INVENTION
Industrial robots are well known in the art. Such robots are
intended to replace human workers in a variety of assembly tasks.
It has been recognized that in order for such robots to effectively
replace human workers in increasingly more delicate and detailed
tasks, it will be necessary to provide sensory apparatus for the
robots which is functionally equivalent to the various senses with
which human workers are naturally endowed, e.g. sight, hearing,
etc.
Of particular importance for delicate and detailed assembly tasks
is the sense of touch. Touch can be important for close-up assembly
work where vision may be obscured by arms or other objects, and
touch can be important for providing the sensory feedback necessary
for grasping delicate objects firmly without causing damage to
them. Touch can also provide a useful means for discriminating
between objects having different sizes, shapes or weights.
Accordingly, various tactile sensors have been developed for use
with industrial robots.
One such tactile sensor, developed by William D. Hillis and John
Hollerback, is disclosed in the article, "How Smart Robots Are
Becoming Smarter", by Paul Kunnucan, High Technology Magazine,
Sept./Oct. issue, pp. 32,36, Technology Publishing Company. This
tactile sensor comprises 256 pressure-sensitive electrical switches
arranged in a 16.times.16 grid pattern. When an object is brought
into contact with the sensor, appropriate switches are triggered so
as to produce a pattern of electrical signals which correspond to
the "feel" of the object contacting the sensor. Hillis and
Hollerback constructed their tactile sensor by sandwiching a piece
of ordinary pantyhose between a top layer comprised of a piece of
non-conductive silicon rubber impregnated with conductive graphite
along 16 parallel lines and a bottom layer comprised of a printed
circuit board having 16 parallel conducting lines disposed therein.
Hillis and Hollerback oriented their top and bottom layers relative
to one another so that the 16 parallel conducting lines in the top
layer were disposed at right angles to the 16 parallel conducting
lines in the bottom layer, thereby forming a sensory array
comprising 256 superimposed intersection points arranged in a
16.times.16 grid pattern. The conducting lines of the top layer are
normally separated from the conducting lines of the bottom layer by
the pantyhose. However, when an object comes into contact with the
sensor and exerts a requisite minimum pressure on the sensor, the
conducting lines make contact with one another through the meshes
of the pantyhose at those intersection points disposed beneath the
points of pressure, thereby allowing current to flow between the
top and bottom layers at selected locations so as to produce a
pattern of electrical signals which corresponds to the "feel" of
the object contacting the sensor.
This same concept is believed disclosed in another publication,
"Active Touch Sensing" by William Daniel Hillis, distributed by the
MIT Artificial Intelligence Laboratory as A.I. Memo 629. In this
second publication, Hillis also describes replacing the
intermediate layer of pantyhose with an alternative separator layer
comprised of non-conductive paint. This non-conductive paint is
sprayed directly onto the bottom side of the top layer as a fine
mist so that it adheres thereto as a collection of spaced,
non-conductive dots. The conducting lines of the top layer are
normally separated from the conducting lines of the bottom layer by
the misted layer of non-conductive paint. When an object comes into
contact with the sensor and exerts a requisite minimum pressure on
the sensor, the conducting lines of the top layer make contact with
the conducting lines of the bottom layer through the gaps existing
between adjacent dots of non-conductive paint at those intersection
points disposed beneath the points of pressure, thereby allowing
current to flow between the top and bottom layers at selected
locations so as to produce a pattern of electrical signals which
corresponds to the "feel" of the object contacting the sensor.
U.S. Pat. No. 4,208,648 discloses another tactile sensor which
comprises 256 pressure-sensitive electrical switches arranged in a
16.times.16 grid pattern, such that when an object is brought into
contact with the sensor, appropriate switches are triggered so as
to produce a pattern of electrical signals corresponding to the
"feel" of the object contacting the sensor. The tactile sensor
disclosed in U.S. Pat. No. 4,208,648 differs significantly from the
aforementioned sensors in many of the particulars of its
construction and operation. More particularly, the sensor disclosed
in U.S. Pat. No. 4,208,648 comprises three distinct layers disposed
in a sandwich arrangement. The top layer is comprised of a
resilient, electrically-insulating material in which is disposed a
first set of 16 parallel conducting lines. The bottom layer is
comprised of a resilient, electrically-insulating material in which
is disposed a second set of 16 parallel conducting lines. The
bottom layer is disposed relative to the top layer so that the
second set of conducting lines extend at right angles to the first
set of conducting lines, thus forming a sensory array comprising
256 superimposed intersection points arranged in a 16.times.16 grid
pattern. The intermediate layer is comprised of a synthetic resin
material which is electrically conductive to some extent in its
natural, unstressed state, and whose conductivity is increased by
compression. When an object exerts a requisite minimum pressure on
the sensor, the conductivity of the intermediate layer is altered
at those locations disposed beneath the points of pressure. As a
result, the current flowing between the first and second sets of
conducting lines is also altered at the locations affected by
pressure, and a pattern of electrical signals is produced which
corresponds to the "feel" of the object contacting the sensor.
Unfortunately, the tactile sensors described above are believed to
suffer from one or more of the following limitations: (1) poor
reliability, (2) poor durability, (3) high cost of manufacture, (4)
significant complexity of manufacture, (5) limited sensitivity, (6)
complicating signal "cross-talk" (where the current signal travels
through the intermediate layer at locations other than those
disposed at the points of pressure) and (7) a pressure/current
relationship of limited utility.
OBJECTS OF THE INVENTION
Accordingly, the principal object of the present invention is to
provide an improved form of tactile sensor which overcomes or
reduces the limitations set forth above.
SUMMARY OF THE INVENTION
These and other objects of the present invention are attained in a
preferred embodiment by providing a tactile sensor which comprises
three distinct layers disposed in a sandwich arrangement. The top
layer is comprised of a flexible, electrically-insulating material
and a plurality of parallel flexible conductive rods. The bottom
layer is comprised of an electrically-insulating material and a
plurality of parallel conductive rods that extend at right angles
to the conductive rods of the top layer, thus forming a sensory
array comprising a plurality of superimposed intersection points
arranged in a grid pattern. The intermediate layer is comprised of
a resilient, electrically-insulating material in which is disposed
a plurality of parallel conductive posts that extend perpendicular
to the planes of the three layers. These posts are comprised of a
resilient conducting material. Each conductive post is disposed at
one of the sensor's aforementioned intersection points so as to
electrically couple one of the conductive rods of the top layer to
one of the conductive rods of the bottom layer. The conductive rods
are formed with a selected cross-section, in order that changes in
the amount of pressure exerted on the sensor will produce
corresponding changes in the contact surface area, and hence a
change in the electrical contact resistance, between the conductive
rods and those conductive posts disposed beneath the points of
pressure. As a result of this construction, the sensor is capable
of better providing a pattern of electrical signals which, through
use of an appropriate computer and computer software, will provide
a determination better approximating the "feel" of an object
contacting the sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of the present invention will
be more clearly described or rendered obvious in the following
detailed description of the preferred embodiment, which is to be
considered together with the accompanying drawings wherein like
numbers refer to like parts and further wherein:
FIG. 1 is a fragmentary perspective view with portions broken away
of the preferred embodiment of the present invention;
FIG. 2 is a sectional view taken along line 2--2 of FIG. 1;
FIG. 3 is a scaled illustration of the cross-sectional shape of the
conductive rods used in the preferred embodiment shown in FIGS. 1
and 2;
FIG. 4 is a block diagram of an electronic control circuit
integrating the present invention; and
FIGS. 5-8 are alternative embodiments of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Looking first to FIGS. 1 and 2, the tactile sensor 2 generally
comprises three distinct layers disposed in a sandwich arrangement:
a top layer 4, an intermediate layer 6, and a bottom layer 8.
Top layer 4 is comprised of a flexible, electrically-insulating
material which is abrasion-resistant. Preferably top layer 4 is
formed out of a polymeric material such as an elastomer, for
example, a blend of polybutadiene and natural rubber, and has a
hardness of between about 50 and 60 durometer on the Shore A-2
scale. Layer 4 has a planar top surface 10 and a planar bottom
surface 12 provided with a plurality of parallel grooves 14. In the
preferred embodiment there are 16 grooves 14.
Each of the grooves 14 has a conductive rod 18A, 18B, 18C, etc.,
secured therein by an adhesive or equivalent means. Rods 18A, 18B,
18C, etc., are formed out of a flexible conductive material.
Preferably rods 18A, 18B, 18C, etc. are made of a polymeric
elastomer, e.g., chloroprene, which is doped with a suitable
conducting material, e.g., carbon black. Rods 18A, 18B, 18C, etc.
are formed so that they have a hardness of between about 70 and 80
durometer on the Shore A-2 scale.
Conductive rods 18A, 18B, 18C, etc., are shaped so that at their
intermediate portions (i.e. those portions of the rods which extend
adjacent intermediate layer 6) each has a cross-sectional profile
generally similar to the cross-sectional profile of a "hull" of a
ship. The cross-sectional profile of the intermediate portions of
rods 18A, 18B, 18C, etc., is shown in greater detail in FIG. 3. As
seen in FIG. 3, the intermediate portions of the conductive rods
are formed with a double curvature of a selected functional
character and have a projecting nose portion 19. Grooves 14 and
conductive rods 18A, 18B, 18C, etc., are sized relative to one
another so that the projecting nose portions 19 of conductive rods
18A, 18B, 18C, etc., extend below the bottom surface 12 of top
layer 4 (see FIG. 2). As will hereinafter be discussed in greater
detail, conductive rods 18A, 18B, 18C, etc. are shaped at their end
portions (i.e. those portions of the rods which project out beyond
the region of intermediate layer 6, so that each has a
substantially rectangular cross-section, as indicated in FIG. 1 at
18'D, 18'E, 18'F, etc.
Bottom layer 8 is comprised of a rigid, electrically-insulating
material such as a non-conducting polymer or the sort of material
typically used to fabricate circuit board substrates, e.g.,
resin-impregnated fiberglass sheets. Layer 8 has a planar top
surface 20 and a planar bottom surface 22, and is provided with a
plurality of flat conductive copper buses 26A, 26B, 26C, etc. In
the preferred embodiment there are 16 buses 26A, 26B, 26C, etc.
Buses 26A, 26B, 26C, etc., are preferably fixed in place on the top
surface 20 of bottom layer 8 by bonding or other equivalent means.
Buses 26A, 26B, 26C, etc., are sized relative to bottom layer 8 so
that an end portion of each bus extends out beyond the end of
bottom layer 8, as shown in FIGS. 1 and 2.
Bottom layer 8 also has a plurality of conductive rods 28A, 28B,
28C, etc., disposed thereon. Conductive rods 28A, 28B, 28C, etc.,
are preferably identical to conductive rods 18A, 18B, 18C, etc.
described above, except that they lack any flat projecting end
portions corresponding to the projecting end portions 18'D, 18'E,
18'F, etc. noted above. In the preferred embodiment there are 16
rods 28A, 28B, 28C, etc. Rods 28A, 28B, 28C, etc., are preferably
fixed in place as shown in FIGS. 1 and 2 by an adhesive or other
equivalent means so that rods 28A, 28B, 28C, etc., make good
conductive contact with buses 26A, 26B, 26C, etc.
Bottom layer 8 is disposed relative to top layer 4 so that
conductive rods 28A, 28B, 28C, etc., extend at right angles to
conductive rods 18A, 18B, 18C, etc., thereby forming a sensory
array comprising 256 superimposed intersection points arranged in a
16.times.16 grid pattern. Preferably conductive rods 18A, 18B, 18C,
etc. are uniformly spaced from one another, and the same is true
for conductive rods 28A, 28B, 28C, etc.
Intermediate layer 6 is comprised of a pad 30 formed out of a
non-conducting elastomeric material such as polyurethane and has a
hardness of between about 40 and 60 durometer on the Shore A-2
scale. Pad 30 has planar top and bottom surfaces 32 and 34.
Intermediate layer 6 also comprises a plurality of
transversely-extending conductive posts 36. Posts 36 extend
perpendicular to the major plane of pad 30 and run between and
intersect the pad's top and bottom surfaces 32 and 34. Conductive
posts 36 are formed from an elastomeric material which is
electrically-conductive. Posts 36 are preferably formed out of a
material of selected conductivity, e.g., a polymer such as
chloroprene compounded with carbon black so as to be conductive,
and have a hardness of between about 50 and 60 durometer on the
Shore A-2 scale. As seen in FIGS. 1 and 2, one conductive post 36
is disposed at each of the sensor's aforementioned intersection
points so as to electrically couple one of the conductive rods 18A,
18B, 18C, etc., of top layer 4 to one of the conductive rods 28A,
28B, 28C, etc., of bottom layer 8.
As seen in FIG. 2, when no force is applied to the top surface 10
of the sensor, only the projecting nose portions of conductive rods
18A, 18B, 18C, etc., contact the conductive posts 36, and only the
projecting nose portions of conductive rods 28A, 28B, 28C, etc.,
contact the conductive posts 36. However, when an object comes into
contact with the top surface 10 of the sensor and exerts a certain
requisite minimum pressure on the sensor, layers 4, 6 and 8 are
forced together so that conductive rods 18A, 18B, 18C, etc., and
conductive rods 28A, 28B, 28C, etc., approach one another at the
points of pressure. As the conductive rods 18A, 18B, 18C, etc., and
the conductive rods 28A, 28B, 28C, etc., are forced together at the
points of pressure, the conductive rods tend to press into the
softer intermediate layer 6 so as to increase their effective
surface area contact with those conductive posts 36 disposed about
the points of pressure. As a result, the electrical contact
resistance established between the conductive rods and those
conductive posts disposed beneath the points of pressure tends to
decrease correspondingly, whereby for a given vltage applied
between rods 18A, 18B, 18C, etc. and rods 28A, 28B, 28C, etc. the
current flow will increase in inverse relation to the changes in
contact resistance.
On account of the foregoing construction, it will be seen that a
pressure-sensitive switch is formed at each of the sensor's
intersection points. When coupled to an appropriate electric
circuit, these switches are together capable of producing a pattern
of electrical signals corresponding to the "feel" of an object
contacting the sensor.
It will be appreciated that the conductive rods 18A, 18B, 18C, etc.
must be sufficiently flexible along their length so that the
localized application of pressure at an intersection point will not
register significantly at adjacent intersection points. At the same
time, however, the conductive rods 18A, 18B, 18C, etc. must have a
sufficient hardness vis-a-vis the components in intermediate layer
6 so that it is the layer 6., and not the conductive rods, which
deforms under the application of pressure. The cross-sectional
geometry chosen for conductive rods 18A, 18B, 18C, etc., and
conductive rods 28A, 28B, 28C, etc. (shown in detail in FIG. 3), is
such that the pressure/current relationship of sensor 2 tends to
have a non-linear response of substantially logarithmic form which
enables it to accurately reflect minute variances of pressure under
very light loads as well as great variances of pressure under very
heavy loads. It is to be noted that the cross-sectional shape of
rods 18A, 18B, 18C, etc. and rods 28A, 28B, 28C, etc. are similar
to the cross-sectional profile of the hole of a ship having
symmetrical double curvatures which work with the nose portions 19
to give the desired effect. It will also be appreciated that the
precise pressure/current relationship of the sensor 2 will depend
also on a number of other factors such as layer thicknesses, layer
compositions, and also the relative hardnesses of conductive rods
18A, 18B, 18C, etc., and 28A, 28B, 28C, etc., and conductive posts
36. By selectively adjusting the aforementioned factors, it is
possible to build a tactile sensor having the desired
sensitivity.
In order to render the tactile sensor 2 substantially impervious to
the effects of certain inhospitable climates, e.g., water or oil,
it is preferred that the edges of top layer 4 and bottom layer 8
extend out beyond the edges of intermediate layer 6, so that the
two may be brought together and joined to form a sealed
environment. More particularly, it is preferred that top layer 4 be
folded down and bonded to bottom layer 8 in the manner shown in
FIG. 2. At the same time, in order to allow the sensor to be
coupled into an appropriate electric circuit, the projecting end
portions 18'A, 18'B, 18'C, etc. of conductive rods 18A, 18B, 18C,
are turned down as shown in FIG. 1 so that they run along the top
surface 20 of bottom layer 8 towards the perimeter of the sensor,
and these projecting end portions (formed with a substantially
rectangular cross-section, as noted above) and buses 26A, 26B, 26C,
etc. extend out beyond the sealed side edges of the sensor, ready
to be coupled to an appropriate electric circuit.
FIG. 4 shows how the preferred form of tactile sensor 2 may be
coupled into an electric circuit for use with an industrial robot.
This circuit generally comprises a computer 50 which is coupled to
the input line of a 16-line demultiplexer 52. Computer 50 is also
coupled to demultiplexer 52 by a control line (shown in phantom).
The 16 output lines of demultiplexer 52 are respectively attached
to the 16 projecting end portions of conductive rods 18A, 18B, 18C,
etc. of sensor 2. The 16 projecting end portions of buses 26A, 26B,
26C, etc., of sensor 2 are respectively attached to the 16 input
lines of a current-to-voltage converter 54. The 16 output lines of
the converter 54 are respectively attached to the 16 input lines of
a multiplexer 56. The output line of multiplexer 56 is coupled to
an analog-to-digital converter 58 and the control line of
multiplexer 56 (shown in phantom) is coupled to the computer 50.
The output from converter 58 is fed to computer 50. The output of
computer 50 is coupled to a robot computer 60, which is itself
attached to robot manipulation controls 62. Robot manipulation
controls 62 control an arm or other robot appendage working in
cooperation with tactile sensor 2. It is to be appreciated that
computer 50, demultiplexer 52, current-to-voltage converter 54,
multiplexer 56, analog-to-digital converter 58, robot computer 60,
and robot manipulation controls 62 are all of the sort well known
in the art.
In a typical case, the sensor 2 is mounted to a robot appendage so
that the rigid bottom layer 8 faces and is fixed to the appendage
and the flexible top layer 4 faces outwardly in position to engage
an object to be handled.
During operation of the robot, the presence of an object on sensor
2 is determined by the control circuit in the following manner. The
computer 50 sends a signal to demultiplexer 52 to energize
conductive rod 18A. Since conductive rod 18A is coupled to each of
the conductive rods 28A, 28B, 28C, etc., by conductive posts 36 at
the sensor's superimposed intersection points, energizing
conductive rod 18A produces a current in each of the conductive
rods 28A, 28B, 28C, etc. However, as previously described, the
current flowing in each of the lines 28A, 28B, 28C, etc. will vary
from one another in accordance with the amount of pressure being
applied to the sensor at the intersections of conductive rod 18A
with conductive rods 28A, 28B, 28C, etc. Converter 54 receives the
current present in each of the conductive rods 28A, 28B, 28C, etc.
by virtue of its connections to buses 26A, 26B, 26C, etc., and
converts the current flowing in each of the conductive rods 28A,
28B, 28C, etc., to a corresponding voltage. The output from
converter 54 is then passed along to multiplexer 56. Computer 50
uses multiplexer 56 as a gating mechanism so as to allow it to
sequentially sample the output from each of the conductive rods
28A, 28B, 28C, etc., and to feed the outputs to converter 58. The
latter converts these analog voltage outputs to digital signals
which are automatically fed to computer 50. Then the computer
orders demultiplexer 52 to deenergize conductive rod 18A and
energize conductive rod 18B. Since conductive rod 18B is coupled to
each of the conductive rods 28A, 28B, 28C, etc., by conductive rods
36 at the sensor's superimposed intersection points, energizing
conductive rod 18B raises a current in each of the conductive rods
28A, 28B, 28C, etc. However, as previously described, the current
flowing in each of the lines 28A, 28B, 28C, etc., will vary from
one another in accordance with the amount of pressure being applied
to the sensor at the intersections of conductive rod 18B with
conductive rods 28A, 28B, 28C, etc. The computer then uses the
circuitry as outlined above to sequentially sample the output
derived from conductive rods 28A, 28B, 28C, etc., and to apply the
outputs to converter 58. This process is repeated over and over,
until the computer 50 has sampled the electrical signals from all
256 intersection points on the sensor and has coordinated the
digital data so as to form a conclusion regarding the presence of
any object on the tactile sensor. The computer 50 then relays this
digital information to the robot computer 60 which automatically
adjusts the robot manipulation controls 62 as needed.
ADVANTAGES OF THE PRESENT INVENTION
The preferred embodiment of the present invention described and
illustrated herein is believed to have numerous advantages over the
prior art.
First, the tactile sensor disclosed herein has a wide range of
sensitivity. The unique geometry of conductive rods 18A, 18B, 18C,
etc., and 28A, 28B, 28C, etc., ensures that the sensor's signal
output will vary logarithmically with contact pressures, in order
that the sensor will be capable of determining minute variances in
pressure under very light loads as well as great variances of
pressure under very heavy loads.
Second, the tactile sensor disclosed herein is relatively reliable,
durable, inexpensive to make, and simple to produce.
Third, the tactile sensor disclosed herein has an intermediate
layer which is conductive only at the sensor's superimposed
intersection points, so that signals can pass between the
conductive rods of the top and bottom layers only at the
intersection points.
Fourth, the tactile sensor is completely sealed from its
environment so as to render it operational under a variety of
threatening conditions.
MODIFICATIONS OF THE PREFERRED EMBODIMENT
It is, of course, possible to modify the preferred embodiment of
the present invention without departing from the scope of the
invention.
Thus, for example, the tactile sensor 2 may be formed with more or
less than 16 conductive rods 18A, 18B, 18C, etc., and more or less
than 16 conductive rods 28A, 28B, 28C, etc. Or the conductive rods
18A, 18B, 18C, etc., and conductive rods 28A, 28B, 28C, etc., may
extend at some angle other than a right angle to each other.
Optionally, conductive posts 36 may be formed with a
cross-sectional shape different than the circular one shown on
FIGS. 1 and 2, e.g., square or other arbitrary shape; similarly,
conductive rods 18A, 18B, 18C, etc., and 28A, 28B, 28C, etc., may
be formed with a cross-sectional shape different than the one shown
in FIGS. 1-3, e.g., triangular.
Furthermore, the sensor's bottom layer 8 need not be stiff or rigid
but may be formed of a flexible material, such as that commonly
used to form flexible circuit boards, or a material the same or
similar to the material of which top layer 4 is made.
Obviously, the way in which the tactile sensor 2 is coupled into
the electric circuit shown in FIG. 4 may also be varied. Thus, for
example, the output lines from demultiplexer 52 may be coupled to
buses 26A, 26B, 26C, etc., and the input lines to converter 54 may
be coupled to conductive rods 18A, 18B, 18C, etc. Also, computer 50
may be programmed to sample the current flowing through the
sensor's intersection points in a sequence other than that
disclosed. Alternatively, sensor 2 may be used with a circuit
entirely different from that shown in FIG. 4.
Referring to FIG. 5, the intergroove material in top layer 4 may be
extended in length as shown at 100 so that the conductive rods 18A,
18B, 18C, etc. do not normally contact the posts 36 disposed in
intermediate member 6. This construction results in the sensor
requiring some non-zero pressure threshold before an electrical
signal can pass between the conductive rods 18A, 18B, 18C, etc. of
the top layer 4 and the conductive rods 28A, 28B, 28C, etc. of the
bottom layer 8.
Alternatively, as shown in FIG. 6, the intermediate layer 6 shown
in FIGS. 1 and 2 may be replaced with a new intermediate layer 6'
comprising a uniform sheet of an elastomeric material which is
conductive, e.g., a silicone rubber layer impregnated with
conductive particles such as particles of carbon, silver, copper
and the like (see U.S. Pat. No. 4,208,648).
Also, as shown in FIG. 7, the conductive rods 18A, 18B, 18C, etc.
and conductive rods 28A, 28B, 28C, etc. may be formed so that they
have substantially rectangular or square cross-sections throughout
their length, and the conductive posts 36 may be formed so that
their projecting ends have cross-sectional profiles similar to the
hull of a ship as previously described in connection with rods 18A,
18B, 18C, etc. and rods 28A, 28B, 28C, etc. Of course, in this
arrangement the rods 18A, 18B, 18C, etc. and 28A, 28B, 28C, etc.
will have a hardness less than the hardness of conductive posts 36,
in order that rods 18A, 18B, 18C, etc. and 28A, 28B, 28C, etc. will
deform under the application of pressure to the face of sensor 2
while posts 36 will remain substantially undeformed.
It is also envisioned, as shown in FIG. 8, that the intermediate
layer 6 could be omitted entirely. In this case the conductive rods
18A, 18B, 18C, etc. would contact conductive rods 28A, 28B, 28C,
etc. directly, and by forming one or both sets of rods from
relatively soft compositions, the requisite pressure variations of
surface area contact (and hence electrical contact resistance)
could be achieved at the affected intersection points.
Furthermore, the sensor may be formed so that only the conductive
rods of the top layer have a hardness greater than the intermediate
layer, or so that only the conductive rods of the bottom layer have
a hardness greater than the intermediate layer.
It is also envisioned that the top surface 10 of top layer 4 can be
textured or have a tread-like contour so as to improve traction.
Furthermore, the sensor need not be planar along its surfaces but
rather each of the surfaces and their associated structure can be
segments of a sphere or cylinder.
These and other similar modifications are believed obvious to one
skilled in the art, and are within the scope of the present
invention.
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